Dimethyl (2,2,2-trichloro-1-hydroxyethyl)-phosphonate, also known as trichlorfon, is an insecticide that is used to control flies, roaches, and turf pests such as webworms, mole crickets and grubworms. Additionally, trichlorfon can be used as an anthelmintic composition for animals.
Generally, the prior art process for synthesizing trichlorfon involves reacting dimethyl phosphite with trichloroacetaldehyde, also known as chloral. The resulting technical material may be purified by recrystallization techniques to generate high purity material, which is greater than 98% pure.
Several processes for making dimethyl (2,2,2-trichloro-1-hydroxyethyl)-phosphonate are known. For example, in one process, 1 mole of dimethyl phosphite is added to 1.15 moles of chloral in a stirred glass-lined stainless steel reactor at a temperature between 70.degree. C.-75.degree. C. The reaction mixture is maintained for 3 hours at 80.degree. C.-85.degree. C. The purification process requires that the resulting molten material be transferred to a stirred glass-lined vessel containing water and recycled mother liquor preheated to 60.degree. C. and then stirred to homogeneity. Water is then evaporated from the diluted reaction mixture by application of a vacuum until the temperature is lowered from 60.degree. C. to 10.degree. C. Crystallization seeding occurs at about 35.degree. C. The slurry is then transferred to another stirred holding vessel and then fed to a centrifuge, where an additional water wash is carried out. The crystalline material is then dried under hot air at 85.degree. C.-90.degree. C. for 7 hours in a drum dryer. The dried material is then passed through a screw conveyor under reduced pressure (200 mm water) prior to being packaged in plastic lined containers.
In another process, Pesticide Manufacturing and Toxic Materials Control Encyclopedia, edited by Marshall Sittig, Noyes Data Corporation, Park Ridge, N.J. 1980, 75 grams of chloral are dropped into 60 grams of dimethyl phosphite at an initial temperature of 25.degree. C. The temperature slowly rises to 50.degree. C. and is kept at 50.degree. C. to 60.degree. C. by external cooling. After cooling the oil is dissolved in benzene, and the benzene solution is washed with a sodium bicarbonate solution and dried with anhydrous sodium sulfate. After the solvent has been distilled off, an oil is left which is almost completely solidified. After washing with an icy mixture of ether and petroleum ether, the trichloro-.alpha.-hydroxyethyl phosphonic dimethyl ester is obtained in the form of colorless needles with a melting point of about 81.degree. C.
In subsequent, but separate processes, the purified and isolated trichlorfon is converted into various manufacturing concentrates, for the purpose of producing the aforementioned end products. As an example of prior art, a dry manufacturing concentrate `trichlorfon 80% concentrate` was registered (EPA) and has been used as the source material for producing `Dylox 5G`, a trichlorfon formulation on maize cob granules. The formulation process involves binding the trichlorfon 80% dry concentrate to the granules using an inert sticking agent (e.g. hexylene glycol). In summary, the overall prior art processes for producing a granular formulation of trichlorfon involve 1) synthesis of technical grade trichlorfon, 2) purification and isolation of trichlorfon, 3) formulation of the recrystallized technical into manufacturing-use concentrates, and 4) binding inert granular carriers with the trichlorfon dry concentrate.
The prior art processes for the production of dimethyl (2,2,2-trichloro-1-hydroxyethyl)-phosphonate are rather complicated and use high quantities of raw materials. Additionally, these processes are expensive because they require 1) higher quantities of reactants, 2) isolation and complicated purification steps, 3) subsequent manufacturing steps for formulating the end-use product formulations, and 4) treatment of waste water from the purification process. Therefore, there is a need in the art for an economical process for producing high purity dimethyl (2,2,2-trichloro-1-hydroxyethyl)-phosphonate, particularly if integrated with a process for direct formulation onto inert carriers.